Circuit breaker contact construction



May 31, 1949. A. s. CASWELL 2,471,608

CIRCUIT BREAKER CONTBCT CONSTRUCTION Original Filed April 22, 1944 3 Sheets-Sheet 1 INVENTOR. HRTHUFZ J. GUM EM BY fl mygw May 31, 19494 A. s. CASWELL CIRCUIT BREAKER CONTACT CONSTRUCTIO N 3 Sheets-Sheet 2 Original Filed April 22', 1944 HSc" /lSb

INVENTOR. 6'7? THUR J. C/IUWHL wry/10 May 31, 1949. A. s. CASWELL CIRCUIT BREAKER CONTACT CONSTRUCTION 3 Sheets-Sheet 3 Original Filed April 22, 1944 INVENTOR. HRTHUR J. CflJWE-ZL see-- Patented May 31, 1949 CIRCUIT BREAKER CONTACT CONSTRUCTION Arthur S. Caswell, Philadelphia, Pa., assignor to I. T. E. Circuit Breaker Company, Philadelphia, Pa a corporation of Pennsylvania Original application April 22, 1944, Serial No.

532,269. Divided and this application November 2, 1946, Serial No. 707,389

4 Claims.

This application is a division of application Serial Number 532,269, filed April 22, 1944, and relates to circuit breaker contact structure for circuit breakers which are constructed to provide a blow-own effect particularly of the arcing contacts; to magnetically blow the are into the arc chute; and to substantially eliminate pigtails in conducting currents into moving members.

In the operation of circuit breakers, it is of co rse necessary to obtain proper contact pressure between the stationary and the movable contacts. Since the movable contact carrying arm has a positive mechanical movement toward the stationary contact, an unpredetermined variation of even minute extent in the length of the stroke of the moving contact arm due to even slight wear will of course interfere with contact pressure.

Accordingly, it has become common to mount the movable contact on the contact carrying arm so that it may pivot or have some other movement with respect thereto and to spring bias the movable contact outwardly away from the contact carrying arm and toward the stationary contact. This spring bias ensures adequate contact pressure even though the length of the stroke of the movable contact carrying arm may vary slightly,

The pivotal mounting of the contact provides an inadequate current conductor from the contact to the contact carrying arm. Accordingly in the past, to ensure good current conduction, a pigtail connection from the contact to the contact carrying arm or from the contact directly to one of the terminals has been necessary.

Where the movable contact was made a rigid part of the contact carrying arm, it was necessary to make the stationary contact member pivotal or otherwise movable with respect to the stationary conductor and to spring bias the same outwardly from the end of the stationary conductor in order to obtain contact pressure. In this case the pigtail connection was required between the stationary contact member and the stationary conductor.

My invention contemplates the construction of a stationary contact member for a circuit breaker which has a pivotal movement with respect to the stationary conductor and is sprin biased outwardly away from the end of the stationary conductor but wherein no pigtail or other shunt connection is necessary in order to provide a current carrying path between the stationary contact and the stationary conductor.

Further, my invention contemplates as an object the provision of means in the mounting of the stationary contact on the stationary conductor for providing a current carrying path directly between the stationary contact and the stationary conductor.

A more specific object of my invention is the provision of means for creating a tight frictional current carrying engagement between the stationary contact and the stationary conductor of a circuit breaker so that a proper current carrying path is provided between them.

While my invention is directed more specifically to the construction and arrangement of a stationary contact member which may be pivotal with respect to the stationary conductor and in which the necessity for pigtail or other shunt connections between the stationary contact and the stationary conductor is eliminated, it will be clear that the structure of the stationary contact may, in appropriate cases, be incorporated in the movable contact structure to perform the same function and to obtain the same results.

My invention also contemplates the arrangement of the arcin contact arm and the mounting thereof in such a manner outside the main contact arm so that the skin effect of the assembly would help the arcing contacts take more current, and, therefore, increase the main contact protection.

A further object of my invention is the arrangement of the arcing contact in such a manner that the inertia thereof will assist in maintaining contact between the arcing contacts during contact opening.

A further object of my invention is the arrangement of the spring and pigtail connections for the arcing contact arm so that they are very near the pivot point of the entire assembly, and so that they will thus have less eifect in slowing down the opening speed of the circuit breaker.

The foregoing and many other objects of my invention will become apparent in the following description and drawings, in which:

Figure 1 is a side view of a circuit breaker contact structure embodying the principles of my Figure 5 is a front view partly broken away of the stationary contact member of Figure 4.

Referring now to Figure 1, the circuit breaker contact structure Iii comprises an upper stationary terminal ii, to which are secured, by means of appropriate bolts E2, the opposite spaced plate extensions i3, i3 (see also Figure 2). The stationary contact block if, hereinafter more specifiically described, is pivotally mounted on a pin It supported between the opposite plates l3, it.

The contact block 85 is provided with a bore 2b in which the compression spring RE is positioned. One end of the compression spring 2i bears against the base of the bore and the opposite end of the spring 2i bears against the leg 22 of the positioning bracket 23.

The positioning bracket 23 is secured to the front end of the stationary conductor ii in any sutiable manner, as for instance by the screws 25. Bracket 23 also has a re-entrant extension 2'! which enters into a slot 28 in the lower end of the contact block E5 to limit both the outward and inward movement of the contact block if, as it rotates about the pin it. That is, when the movable contact is moved away from the stationary contact, the spring 25 drives the lower end of the stationary contact block it to the right until the left hand wall of slot 28 bears against the re-entrant flange 21.

The right hand Wall of slot 26 ensures that the movable contact block l5 will not be rotated to the left for so great a distance as to result in injury to the spring 2i or damage to the stationary contact structure.

The contact block i5 is provided with a main contact surface 39 and an arcing contact surface 3!. The main contact surface 3% is engaged by the movable main contact 32 which is positioned on the movable contact arm 38.

The arcing contact surface 3 i' is engaged by the movable arcing contact 33. Arcing contact arm 36 is pivotally mounted on the pin 82' carried by the movable contact arm 38 and is provided with an arcing horn 35 along which the arc is ma netically driven. The lower end of the arcing contact arm 36 is provided with a spring bias (hereinafter described) which tends to rotate the arcing contact arm 36 in a counterclockwise direction so that the arcing contact 53 is biased to the left.

The contacts 3! and 33 will therefore engage before the contacts 30 and 32. The arcing contact arm 36, as will move readily be seen in Figure 3, is actually a compound arm 36a and 36b mounted on either side of the movable contact arm 38.

The pin 3'! passes through an opening in the movable contact arm 38; and the arcing contact arms 36a and 36b are rotatably mounted on the said pin 31. The two arcing contact arms 36a and 362) are connected by a bridging plate ii]. The movable contact carrying arm 38 itself also consists of two arms 38a and 3% (see also Figure 3) which are connected together at their upper end by the contact block 45 so that they operate together.

A bolt 55 is secured in any suitable manner to the center of the bridging plate (it which interconnects the arcing contact arms 345a and 36b, and this bolt passes between the movable contact carrying plates 33a and 38b and projects beyond the front of the movable contact arm. An additional pin 36 interconnects the two movable contact arms 38a and 38b'and pivotally receives the 4 link 24 which operates the contact bridge 38 between the open and closed position by means of an appropriate operating mechanism.

A compression spring El surrounds the bolt 55 and is compressed between the bridging plate M3 and the head 53 of the threaded bolt 55. The opposite end of the bolt 55 is provided with a plate 42 which bears against the front surface of the main contact bridge arms 38a and 38b and is secured in place with respect to the plate 42 by means of the nut 43. A lock-nut 59 maintains the predetermined adjustment. The compression spring therefore biases the arcing contact arm 35 toward counterclockwise rotation so that the movable arcing contact 33 is biased outwardly toward the left of the movable contact arm 38.

A pigtaial 6B is connected between the arcing contact arm 35 and the pigtail boss 4?. It will, of course, be clear that a separate pigtail 66 is provided on each side. The plates 33a and 38b of the movable contact arm are mounted on either side of the lower stationary conductor 62. A bolt 63 passes through appropriate registering openings in the contact arm plates 38a and 38b, and in the stationary conductor t2.

A spring washer t t of highly conductive material is placed between the head of the bolt 6.? and the contact arm plate 38a on one side of the structure and an additional washer E5 of similar material is placed between the nut 66 of the contact arm plate 382) on the other side of the structure. The nut E55 is tightened and secured in tightened position.

Contact arm 38 comprising plates 38a and 38b now has rotative movement around the shaft of the bolt 63. The inner surfaces of the plates 38a and 381) are in tight frictional engagement with the outer surface of the lower conductor 82, thus creating an appropriate current carrying path between the movable contact arm 38 and the lower conductor 62.

In order further to ensure an appropriate current carrying relationship between the lower conductor 62 and the lower ends of the plates 38a and 331), additional washers 61 and 68 may be placed between the lower conductor 62 and the plates 38a and 38b.

The current carrying path between the contact arm 38 and the lower conductor 62 is essentially a divided path. A portion of the current passes from the outer surface of each of the plates 35a and 38b to the spring washers 64 and 65, then to the head of the bolt 63 and the nut 66, then to the shaft of the bolt and through the shaft of the bolt to the lower conductor 62. The remainder of the current passes directly from the inner surfaces of plates 38a and 381) through the washers El and 68 to the surface of the lower conductor 62. By this means a pigtail connection between the movable contact arm 38 or the movable contact 32 to the lower conductor 62 is obviated.

The pigtail fit between the arcing contact arm 36 and the movable contact arm 33 may be obviated in a similar manner by providing for a similar mounting at 37 of the contact arm 36 on the movable contact arm 36, although in order to provide a freely rotatable bearing surface at 3?, the actual current path in Figure 1 is provided by the pigtail lit in Figure 1.

As seen more particularly in Figure 2, the stationary contact block it is made up of two contact fingers l5a and ltib. Contact fingers lion and 551) are rotatably mounted on the pin l6 between the plates l3, 83 as above pointed out.

Each of the contact fingers a and I5!) is provided with a lateral opening ill through which the pin l6 passes.

The inner surface of each of the contact blocks I 5a and IE2) is counterbored at H to produce two co-axial and adjacent openings which register with each other to form a single continuous housing for the compression spring 13. Compression spring 73 bears against the opposite bases of the counterbore 'H to drive the contact fingers [5a and 15b apart. A spacer washer T5 of highly conductive material is provided around the pin 56 between the outer surface of each of the contact fingers i5a and |5b to provide an efiicient current carrying path between the respective contact fingers to the plates l3, 13. The compression spring 73 thus ensures that the contact block 55 comprising the contact fingers i511 and 1% will be in appropriate current carrying relationship with the plates i3, l3 and hence with the upper stationary conductor II.

By this means therefore, although the main stationary contact 3% is pivotal around the pin [6 and is provided with a spring bias urging it away from the upper stationary conductor ll, nevertheless a pigtail connection from the main stationary contact 3%} to the upper stationary conductor H is made unnecessary. The spring 13 and the spacer washers l5 provide for such a current carrying path. Since the main stationar contact at is thus provided with the necessary spring bias to ensure appropriate contact pressure, the main movable contact 32 may be rigidly secured to the movable contact arm 38.

Since, however, the stationary arcing contact tip ii! is mounted on that portion of the contact block l5 which has relatively the smallest amount of rotation and has substantially no inward or outward movement with respect to the upper stationary conductor H, the movable arcing contact 33 is mounted on the pivotal arm 35 and is provided with the necessary spring 5? to ensure proper arcing contact pressure.

As will now be obvious, when the circuit breaker is open, the arcing contact 33 is rotated to a substantial extent counterclockwise with respect to the movable contact arm 88 by means of the spring 51 so that the arcing contact tip 33 projects substantially beyond the movable main contact 32.

Accordingly on a closing operation of the circuit breaker the arcing contacts 3! and 33 will meet first. On completion of the closing movement however the main movable contact 32 moves into engagement with the main stationary contact 3!), the contact block it is rocked about its pivot l6 compressing spring 2! until the right hand side of slot 28 engages re-entrant flange 21. At the same time the spring 5'! on the movable contact arm which applies the necessary bias to the arcing contact tip 33 is progressively compressed.

On the initiation of the opening movement of the movable arm 33, movabl contact 32 will move to the right followed by contact 3?) under the action of spring 2! until the left wall of the slot engages projection 21. Thereafter contact 32 will separate from the stationary main contact while the spring 5! maintains the movable arcing contact tip 33 in engagement with the stationary arcing contact tip 3!. When the base of the U-shaped bracket 48 moves into engageent with the back surface of the movable contact arm 38, then the movable arcing contact 6 will be withdrawn from engagement with contact 3i. It will thus be seen that the arcing contacts open last in order to protect the main contact surfaces. This is obtained of course by the spring bias of compression spring 57, as above pointed out.

This result is also obtained, however, by reason of the mechanical arrangement of the arcing contact arm 35. As is well known, current in the loop formed by the conductor 62, the contact arm 38 and conductor H provides a magnetic force tending to rotate the movable arm 38 clockwise about its pivot. On short circuit this blow off action assists in the disengagement of contacts 32 anad 38.

This same magnetic action acting on arm 36 will provide a rotative force on the arcing contact arm 36 driving the part of the arm below pivot 37 in a counterclockwise direction, and the part of the arm above pivot 3? in a clockwise direction. However, since leverage for the portion below the pivot 37 includes not only the arm 86 but also the pigtail Ell extending down to the conductor 62, the total force providing the counterclockwise rotation about pivot 31 is greater than the force tending to produce a clockwise rotation.

Accordingly, the net magnetic force of the short circuit current is to drive the arcing contacts 3i and 33 into engagement while the main contacts separate. This force added to that produced by the compression spring 57 already described insures a firm arcing contact engagement during the initiation of contact separation.

Thus the arc will be drawn at the arcing contacts only and the main contacts will be protected.

The design of the stationary contacts as has above been pointed out obviates the necessity for any pie-tail or shunt connections of any kind whatever. These contact structures have been found under test to operate elficiently with only normal temperature rise. The only possible disadvantage which at least for the present is theoretical rather than actual, is that the two parallel fingers carrying the parallel currents may be magnetically attracted under conditions of very high short circuit to such an extent that they may be pulled out of contact. The construction shown in Figures l and 5 obviates even this possibility. In Figures 4 and 5, I have shown a modified form of stationary contact structure within the spirit of my invention. It is suflicient to point out, however, that the movable contact members which cooperate with the stationary contact members shown in Figures 4 and 5 are fully rigid, that is, both the movable arcing and movable main contact are rigidly secured to the movable contact arm.

In Figure 4, the upper stationary conductor or main connection stud is a simple rectangular bar IN. A pair of contact arms 5a and H51) are mounted on either side of the upper connected stud l l l and are rotatably secured thereto by means of the bolt l [6 which passes through the opposite arms 5a and [15b and through the connection stud ll l. A spring washer I 64, I66 is mounted on either side between the head ill] of the bolt H6 and contact plate H51) and between the nut I'H of the bolt H6 and the contact plate a. Contact plates H511 and 5b are provided at their lower end with the main stationary contact tips I30, I30. An appropriate current carrying path, as above pointed out, is provided from the main stationary contact tips 7 I30 through the plates I la and I I5!) to the conductor I I I, so that no pigtail or shunt connecting members are required.

An appropriate contact pressure is provided for by means of the pin Hill which bears against the flange II on each of the plates I We and I I52) on each side of the conductor III. The pin I 4% is biased for movement toward the flange Isl in order to obtain the necessary contact pressure by means of the compression spring IBI. A bolt I 31 passes between the plates H501. and H51) at the upper end of each thereof and supports the stationary arcing contact I36 at the end of which the stationary arc tip [SI is located. The bolt I3! is also provided with spring washers I55 so that on tightening of the bolt, appropriate current carrying engagement is created between the arcing contact member I55 and the plates H50: and H51).

A pin I 56 is mounted between the plates HM and I I5b at the upper left end thereof. The said pin supports a block I561; through which the link I55 passes. Link I55 is pivotally connected at the opposite end to the pin Idll passing between the arcing contacts I35. A compression spring I 51 is mounted between the block I5ta and a boss I58 on the link I55 adjacent the arcing contacts I 36. The compression spring thus tends to rotate the arcing contact I35 counterclockwise so that the arcing contact tip ISI tends to move outwardly. This outward movement is limited by the adjustable nut I as mounted on the outer threaded end of the link I55 which may be secured in appropriate adjusted position by the locknut I59a. It will here be obvious that as the movable contact arm brings the movable contacts into engagement with the stationary contacts, the movable arcing contact will first engage the stationary arcing contact Isl. Then on continued movement toward closing position of the movable contact arm, the spring I51 will be compressed so that the stationary arcing contact tip I3I will move to position shown in Figure 4, whereupon the main stationary contact I30 will be engaged by this complementary contact.

On continued movement of the movable contact arm, the contact plates H505 and H51) will be rotated counterclockwise around the pivot lit to compress the spring IBI, thus ensuring appropriate contact pressure. The current from the plates H511 and H517 will pass readily to the stationary conductor III by means of the bolt H6 and the washers the as above pointed out. Similarly the current from the arcing contact I36 will pass to the plates H511 and M5?) by means of the bolt I31 and the spring washers I65, as above pointed out, and thence also to the conductor III. By this means therefore the necessity for utilization of any pigtail or shunt connections in the entire circuit breaker contact structure is obviated.

Also, it will be seen that since the contact plates I I5a and H51) are on the outside of the stud III and of the arc tip Isl, parallel current will pull them together and increase the contact pressure thus avoiding the theoretical disadvantage of the structure shown in Figure 2.

The contact plates H511 and H51) are limited in movement with respect to the conductor III by reason of the fact that the conductor III is provided with a reinforced slot I28 passing therethrough and which engages the pin IZTI in each of the plates 5a and M51). The cooperation of the pin I2! and the slot I 28 will limit inward and outward movement of the lates I Mia and I I5!) in the manner similar to that described in connection with the slot 28 and the re-entrant extension 2'I of Figure 1, and for the purposes therein set forth.

The arcing contact arm plates 36a and 361) are each provided with a frontwardly projecting lug 5th, through which the mounting pin 37 passes, which secures them to the main movable contact arm 38.

The main movable contact arm 38 is provided with a rearward extension 52 at the end of which the main movable contact 32 is mounted. This extension is so arranged that a substantial clearance 55 is provided between the rear surface 54 of the main arm 33 and the front surface 58 of the arcing contact arm 35.

To ensure a good conducting path for short circuit currents, the arcing contact arm 36 is connected by the pigtail connections Bil to the lower conductor 5'2.

As will also be obvious, the current in the contact arm is in the same direction as in the arcing contact arm Thus, the lower end of arm 38 below the pivot point 3? is attracted magnetically to the arm 38.

The provision of the clearance it between these arms, by reason of the shape thereof, causes this attraction to exert a counterclockwise force on the end of the arcing contact arm 38 below the pivot This of course, increases the contact pressure between the arcing contact tips 3| and 33.

By this means, therefore, when main contact separation occurs under short circuit conditions (due to the current which still flows over arm 36 and through pivot 37) this arrangement further ensures that the arcing contacts will continue to remain in engagement for the longest possible period after the main contacts have separated.

As will also now be clear, the portion of the arcing contact arm as below the pivot point 31 being substantially greater than the portion of the arm 38 above the pivot point 31, the magnetic forces produces by the current loop reacting on the portion of the arm 35 below the pivot point 3'1? causes a further blow on effect.

In addition, it will be obvious from Figures I and 3 that the arcing contact arms 36a and 35%) are outside the main bridging plates 38a and 3%, so that the skin effect of the assembly would help the arcing contacts take more current and increase the main contact protection.

Furthermore, the portion of the arcing contact arm 36 above the pivot point 3?, owing to its position (its mass is closer to the pivot 31 than is the mass of the portion of the arm below the pivot 3?), has a greater inertia effect than that portion of the arcing contact arm 35 below the pivot point 3? and thus aids in maintaining the arcing contacts in engagement during the opening of the circuit breaker.

Furthermore, the spring 5i and the pigtail 60 of the arcing contact arm 35 are very near the assembly pivot so that they have less eifect in slowing the opening speed of the circuit breaker as a whole.

In addition, this structure has the advantage that the direction of the current in the moving arcing tip is in the direction to drive the current to the upper end of the tip, by its own magnetic field, thus hastening the movement of the arc into the arc chute (not shown) and its rupture there.

In the foregoing, I have described my invention only in connection with preferred embodi- 9 ments thereof. Many variations and modifications of the structure, arrangement and uses of my invention should now be obvious to those skilled in the art. Accordingly, I prefer to be bound not by the specific disclosures herein but only by the appended claims.

I claim:

1. A circuit breaker structure comprising a terminal, opposed spaced plate extensions secured to said terminal, a pair of stationary contact juxtaposed blocks having a slot in one end thereof, a pin supported between said plate extensions, said contact blocks being pivotally mounted on said pin, a movable contact arm having main and arcing contact surfaces, said contact blocks having main and arcing contact surfaces, the main contact surface being engageable by the movable main contact surface and the arcing contact surface being engageable by the movable contact surface, said contact blocks being each provided with a bore, a positioning bracket secured to one end of said terminal, said bracket having a reentrant extension entering said slot, a compression spring positioned in each of said bores, one end of said compression spring bearing against the base of its bore and the opposite end bearing against said positioning bracket for biasing said contact blocks toward said movable contact, said re-entrant extension in said slot limiting the outward and inward movement of said contact blocks on said pivot pin, said contact blocks each having a bore extending from their engaging surfaces coaxial with each other and forming a continuous bore, a compression spring mounted in said continuous bore for biasing said contacts apart, a highly conductive spacing washer mounted between said contact blocks and said extension plates, said compression spring driving said contact blocks against their respective extension plates to form good electrical contact therewith.

2. A circuit breaker structure comprising a terminal, opposed spaced plate extension-s secured to said terminal, a pair of stationary contact juxtaposed blocks having a slot in one end thereof, a pin supported between said plate extensions, said contact blocks being pivotally mounted on said pin, a movable contact arm having main and arcing contact surfaces, said contact blocks being each provided with a bore, a positioning bracket secured to one end of said terminal, said bracket having a re-entrant extension entering said slot, a compression spring positioned in each of said bores, one end of said compression spring bearing against the base of its bore and the opposite end bearing against said positioning bracket for bias- 10 a ing said contact blocks toward said movable contact, said re-entrant extension in said slot limiting th outward and inward movement of said contact blocks on said pivot pin, said contact blocks having main and arcing contact surfaces, the main contact surface being away from said pivot and in the movable part of said contact blocks, and the arcing contact being adjacent said pivot.

3. A circuit breaker structure comprising a terminal, opposed spaced plate extensions secured to said terminal, a pair of stationary contact juxtaposed blocks, said contact blocks each having a bore extending from their engaging surfaces coaxial with each other and forming a continuous bore, a compression spring mounted in said continuous bore for biasing said contacts apart, a highly conductive spacing washer mounted between said contact blocks and said extension plates, said compression spring driving said contact blocks against their respective extension plates to form good electrical contact therewith.

4. A circuit breaker structure comprising a terminal, a contact block in electrical engagement with said terminal, a pivot, said contact block being pivotally mounted on said pivot, an arcing contact surface on said block adjacent said pivot, a main contact surface on said block furthest from said pivot and in the movable portion of said block as said block rocks on said pivot, a first movabl arm carrying an arcing contact surface in engagement with said arcing contact surface on said block, a second movable arm carrying a main contact surface in engagement with said main contact surface on said contact block when said movable arm is in circuit breaker closing position, said first movable arm being pivoted on said second movable arm, a spring biasing said contact block main contact surface into engagement with said movable main contact surface and a spring biasing said movable arcing contact surface into engagement with the arcing contact surface on said block.

ARTHUR S. CASWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,208,411 Crabbs July 16, 1940 2,214,471 Ludwig et al Sept. 10, 1940 2,276,786 Lindae Mar. 17, 1942 2,281,752 Cumming May 5, 1942 

